A Lab-on-Chip device is a subset of Micro Electro-mechanical System (“MEMS”) device, also referred to as micro-device, and typically used to miniaturize bio-chemical analysis and synthesis. Micro-devices include micro-features such as micro-channels, micro-capillaries, micro-mixers, micro heaters, and/or micro-chambers. Two or more substrates are bonded together such that the micro-features in one substrate are aligned with micro-features on the second substrate to form, for example, a micro-capillary. Such micro-capillary can accommodate fluids (such as liquids and/or gases) to be transported or stored, with the intention to perform a chemical reaction between constituents of the fluid, or to separate or mix constituents of portions of the fluid, and subsequently perform chemical or physical analysis on the constituents of the fluid, either on or off the chip.
Certain advantages of micro-devices compared to conventional systems include low operating costs (due to miniscule volumes of reagents used), faster response time due to high surface to volume ratio, possibility of mass parallelization due to small size, and lower fabrication costs due to mass production. Furthermore, micro-reactors within such micro-devices offer certain additional benefits over conventional scale reactors, for example, high energy efficiency, reaction speed and yield, safety, reliability, scalability, on-site/on-demand production, and better process control capabilities.
Typically, present day micro-devices are manufactured using silicon substrates. Manufacturing on a silicon substrate is well-established process derived from the micro-electronic semiconductor industry. However, producing such micro-devices using traditional process on silicon substrates incur high production costs. For example, silicon micro-devices that needs to be configured for handling chemical or biological sample needs to implement CMOS-like processes and further processes such as surface treatment to achieve biocompatible micro-features. Such processes make the conventional manufacturing process expensive.
Furthermore, conventional techniques use sealing methods that dispense polymer forming liquids, such as epoxies and the like, that are undesirable for micro-devices used in chemical or biological applications. For example, dispensing a uniformly thick material layer on exact positions along the periphery of an engraved micro-feature is extremely difficult. Further, properties of such sealing materials such as porosity, mechanical integrity, and interference of the material with organic solvents within the micro-features pose certain challenges during operation of the micro-devices. Furthermore, such sealing methods have the disadvantages that an electric field is required for bonding.
The above methods are not suitable where sealing is required on metal patterns that are present in-between the two substrates. Sealing over metal micro-features that are extended over one of the substrates may result in liquid leakage even after a careful heat treatment during the thermal bonding procedure. The prevention of leakage is crucial for fluidic systems, since leakage can give rise to cross-talk between adjacent fluidic conduits and leads to dead-volumes that give rise to cross-contamination of subsequent samples. Prevention of leakage is particularly important in fluidic systems which are to be used for gas analysis, systems in which gases are formed by reaction in the channel, or systems in which gas is introduced into a liquid in order to perform a chemical reaction on a chip, such as in micro-reactors for high-throughput screening of chemical substances.
Therefore, there is a need for a scalable manufacturing technique that is capable of forming micro-features on substrate that are relatively passive towards chemicals and gases used for analysis. Further, there is a need for a simple and efficient bonding between two such substrates to form a leak-proof micro-device.